Process for production of organomercury perthiocyanates



Patented Oct. 17, 1950 .PROCESS FOR PRODUCTION OF ORGANO- MERCURY PERTHIOCYANATES 4 William H. Hill, Pittsburgh, Pa., 'assignor to Koppers Company, Inc., Pittsburgh, Pa., a cor- 'poration of Delaware No Drawing. Application August 18, 1948,

Serial No. 44,991

' 6 Claims. (Cl. 260 299) This invention relates to a chemical process and is particularly directed to the manufacture of organomercury perthiocyanates.

organomercury salts are commonly prepared by what is known as a solubility reaction. In this reaction the desired organomercury salt is obtained as a precipitate from a solution in which the desired organomercury radical is introduced as a more soluble mercury salt together with an acid or salt thereof corresponding to the desired organomercury salt. A characteristic feature of this process is the use of a mutual solvent for both reagents, and because the most desirable mutual solvents are organic solvents it is necessary to the economy of the process to I recover the solvent before recycling.

a suitable acid is utilized in the preparation of Q organomercury perthiocyanate, the product tends progressively to become darker as the mutual solvent is recycled. It appears that in the treatment of the salt of thiocyanic acid with acid by-products contaminate the perthiocyanic acid and build up in the recycled mutual solvent sufficiently adversely to affect the character of the product obtained.

I have now found that this difficulty is avoided by treating the crude perthiocyanic. acid with only a part of the alkali. necessary to convert it to a salt of perthiocyanic acid while it is suspended in a mutual solvent for this perthiocyanic acid salt and the reagent organomercury compound, effecting a mechanical separation of the undissolved perthiocyanic acid in thissolution andthen introducing the reagent organomercury compound. When the process is carried out in this wise I have found that the solvent may be separated from the precipitated organomercury perthio'cyanate and recycled in the process without deleteriously affecting the character of the product.

Since there are many types of organic mercury compounds I desire to reserve the term organomercury as referring to a compound in which mercury is linked to an organoradical by a covalent link. Mercuric acetate, therefore, would not be an organomercury compound because-both valencies of the'mercury are satisfied by electrovalent bonds. ,Organom'ercury compounds are of two types; namely, primary and secondary. Secondary organomercury compounds are those in which both valencies of the mercury are covalent. Compounds of this type are generally designated by the type formula R-Hg--R. Primary organomercury compounds are those in which only one of the mercury valencies is covalent. These compounds are represented by the type formula .R.Hg--X. The organomercury-compounds utilized and produced in the process of the invention areof the latter type, i. e., they are primary organomercury compounds. In other words, they .are compounds in which one valence is: a pair of shared electrons uniting an organic radical with the mercury, and the other valence is an electrovalent bond linking the mercury with an electrovalent radical or an anion.

The processes of the invention are generally applicable to the manufacture of organomercury perthiocyanates independently of the nature of the organic radical. Since the organic radical and the mercury atom are united by a covalent bond into a stable radical which remains unchanged in the process, the nature of the organic part of this radical is of little consequence, insofar as the process is concerned, as long as it' does not, itself, enter into reaction with any of the constituents of the reaction medium. The only requirement as to the organic part of the organomercury radical, therefore, is that it be inert speaking with reference to the process involved. The organic radical may be aliphatic or 'cycloaliphatic, saturated or unsaturated; it maybe aromatic or heterocyclic. Thus it may be alkyl, cycloalkyl, aryl, aralkyl, any of which may be substituted with indifferent substituents, i. e., substituents which go unchanged or unaltered through the "reaction.

The nature of the electrovalent radical or anion of the reagent organomercury compound likewise is not vital. All that is required in this respect is that it be united with the organomercury radical by an electrovalent bond, and that the organic mercury compound itself be a soluble one. When I speak of the reagent organomercury compound as being soluble, I mean that it is soluble as compared with the desired organomercury perthiocyanate. I'n solubility reactions of the type here involved, the progress of the reaction depends essentially upon the'relative solubility of the reagent organomercury compound as compared with that of the product organomercury compound. As long as the latter is insoluble, i. e., as compared with the former it will precipitate out at the expense of the other if a suitably concentrated solution is maintained. The absolute solubility is not important except as it affects the volume of solvent -required' for effecting the reaction. Nor is 'theconcentration of thesolutionimportant except, of course, that it must be sufficient so that the supersolubility concentration for the product organomercury perthiocyanate is ex-,

ceeded. These principles are well known in the art and are inherent in the successful operation of any solubility reaction.

The perthiocyanic acid which is utilized in the processes of the invention and which gives I'lSB to the diificulty above described is obtained by the action of a suitable acid on a salt of thiocyanic acid. In a typical preparation, molal proportions of ammonium thiocyanate and sulfuric acid in the form of 60% and 75% aqueous solutions respectively are gradually admixed by adding the acid to the salt solution at a rate adapted to maintain the temperature of the admixture at between about 35 C. and 40 C. After standing at room temperature for about 120 hours in admixture, the yellow precipitate of perthiocyamc acid is filtered off and washed free of soluble salts either on the filter or by resuspension in water. In place of these reagents any salt of thiocyanic acid may be used along with any acid which will liberate thiocyanic acid therefrom. The thiocyanic acid apparently polymerizes to the dimer and the trimer and then converts over to perthiocyanic acid with the splitting out of hydrocyanic acid.

The nature of the contaminant which gives rise to the above described difficulties is not known. No trouble is encountered, however, if the crude perthiocyanic acid is recrystallized from water or is extracted with carbon disulphide. When the crude acid is not thus refined, however, the product organomercury perthiocyanate is discolored by a dark colored precipitate, and especially so after the solvent used has been recycled a number of times.

The invention may be more fully understood by reference to the following example in which.

the parts are by weight unless otherwise understood. This example is' given by way of illustration, and is not intended to be a measure of the scope of the invention. Within the limits which have already been described and as will be more particularly pointed out, other reagent organomercury compounds may be substituted for the phenyl mercury acetate to produce the corresponding organomercury perthiocyanate without.

changing the process other than as may be required by the diiferent molecular weights of the.

product involved.

Example 100 parts of crude perthiocyanic acid obtained as above described by the interaction of ammonium thiocyanate and sulfuric acid was suspended in 1,630 parts by weight of 95% ethanol. While agitating the ethanol to maintain the suspension, ammonia gas was bubbled into the solution until the weight had increased by 19 parts. This was equivalent to 85% of the theoretical amount of ammonia required completely to neutralize the crude perthiocyanic acid on the basis that two mols of ammonia is required to neutralize one mol of the acid. The ammoniated solution thus prepared was filtered and poured into a solution of 312.6 parts of phenyl mercury acetate dissolved in 16,300 parts by weight of 95% ethanol at 60 C. The phenyl mercury acetate was dissolved in the ethanol at 60 and the ammoniated solution which was at room temperature was poured into the alcohol solution while at 60 C. A yellow precipitate formed immediately and was immediately filtered Off. The alcohol was then recycled as solvent in the neu- 4 tralization'and as solvent for the phenyl mercury acetate. After three cycles there was no evident discoloration of the product.

In place of phenyl mercury acetate there may be used phenyl mercury hydroxide or other salts of phenyl mercury hydroxide such as phenyl mercury chloride and phenyl mercury bromide. The phenyl mercury acetate also may be replaced by other organomercury compounds such as ethyl mercury bromide, ethyl mercury chloride, ethyl mercury phosphate, homologous compounds thereof such as the propyl, isopropyl and like alkyl mercury salts or alicyclic mercury salts such as the cyclohexyl mercury halides as well as homologous alicyclic compounds. Also, there may be substituted homologous aromatic organic mercury compounds. In'. short, there may be substituted any soluble primary organomercury compound in which the organic radical is non-reactive in the process.

In place of ammonia there may be used other alkali including alkali metal ba:es such as sodium and potassium hydroxides and hydroxides of other metals capable of forming soluble salts with perthiocyanic acid such as the hydroxides of calcium, barium and strontium.

I claim:

1. in a process for the manufacture of organemercury perthiocyanates from crude perthiocyanic acid obtained from the action of an acid on a salt of thiocyanic acid in which the desired organo-mercury perthiocyanate is obtained as a precipitate by means of a solubility reaction involving a salt of perthiocyanic acid and a soluble pr1mary organomercury compound; the steps of neutralizing the crude perthiocyanic acid with a quantity of alkali insufiicient to convert all the perthiocyanic acid to, a salt while the perthiocyanic acid is suspended in a mutual solvent for the perthiccyanic acid salt and said soluble primary organomercury compound, filtering the solution thus obtained to remove any undissolved per thiocyanic. acid, 'and introducing into the clear solution thus obtained said soluble primary organomercury compound whereby the desired organomercury perthiocyanate is precipitated, separating the precipitate from the solution and recycling the thus recovered solvent to said neutralizing step.

.2. The process of claim 1 in which equals phenyl.

3. The process of claim solvent equals ethanol.

4. The process of claim solvent equals ethanol.

5. The process of claim equals ethyl.

6. The process of claim equals ethyl.

2 in which mutual l in which mutual 4 in which organo 1 in which oreano WILLIAM H. HILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain May 26, 1930 

1. IN A PROCESS FOR THE MANUFACTURE OF ORGANOMERCURY PERRTHIOCYANATES FROM CRUDE PERTHIOCYANIC ACID OBTAINED FROM THE ACTION OF AN ACID ON A SALT OF THIOCYANIC ACID IN WHICH THE DESIRED ORGANOMERCURY PERTHIOCYANATE IS OBTAINED AS A PRECIPITATE BY MEANS OF A SOLUBITLITY REACTION INVOLVING A SALT OF PERTHIOCYANIC ACID AND A SOLUBLE PRIMARY ORGANOMERCURY COMPO9UND; THE STEPS OF NEUTRALIZING THE CRUDE PERTHIOCYANIC ACID WITH A QUANTITY OF ALKALI INSUFFICIENT TO CONVERT ALL THE PERTIOCYANIC ACID TO A SALT WHICH THE PERTHIOCYANIC ACID IS SUSPENDED IN A MUTUAL SOLVENT FOR THE PERTHIOCYANIC ACID SALT AND SAID SOLUBLE PRIMARY ORGANOMERCURY COMPOUND, FILTERING THE SOLUTION THUS OBTAINED TO REMOVE ANY UNDISSOLVED PER THIOCYANIC ACID, AND INTRODUCING INTO THE CLEAR SOLUTION THUS OBTAINED SAID SOLUBLE PRIMARY ORGANOMERCURY COMPOUND WHEREBY THE DESIRED ORGANOMERCURY PERTHIOCYANATE IS PRECIPITATED, SEPARATING THE PRECIPITATE FROM THE SOLUTION AND RECYCLING THE THUS RECOVERED SOLVENT TO SAID NEUTRALIZING STEP. 